The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and th...The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.展开更多
The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects ...The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.展开更多
Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport...Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport （SST） turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.展开更多
基金supported by National Outstanding Young Scientists Funds of China (Grand No.50825902)
文摘The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.
文摘The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.
基金supported by the National Natural Science Foundation of China(Grant No.51009077)the National High Technology Research and Development Program of China(863 Program,2009AA05Z424)
文摘Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport （SST） turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.
